This invention relates to a power semiconductor device, and more particularly to a power semiconductor device adopted to limit a current flowing through a load.
Generally, it is widely adopted for limiting a load current flowing through a power semiconductor device to control a voltage or a current applied to a control terminal of the semiconductor device. Here, however, the characteristic curve between the flowing load current and the control signal is non-linear such as a quadratic curve. Thus, it is difficult to control the current flowing through a semiconductor element only by a control signal applied to the control terminal thereof. Particularly, since the characteristic curve rises sharply at large load current values, it is very difficult to control the load current at a high precision. It is also adopted for controlling a load current flowing through a semiconductor element, to insert a resistor in series to the semiconductor element, detect the voltage drop appearing across the resistor and to adjust the control signal based on the voltage drop. In such a configuration, however, the power dissipation in the series resistor becomes large and generates much heat which is not favorable for the semiconductor device.
U.S. Pat. No. 4,553,084 proposes a metal-oxide-semi-conductor (MOS) device having a plurality of current paths, wherein part of a load current flowing through part of the current paths is detected to control the total load current. In this MOS type power semiconductor device, a current detecting resistor is connected to part of thousands of circuit elements of the MOS semiconductor device, part of the load current is detected as the voltage drop across the afore-mentioned current detecting resistor, and the voltage signal applied to the gate terminal is controlled on the basis of the detected voltage drop. Whereby it is intended to minimize the power dissipation and to control the load current with a high precision.
Meanwhile, the so-called electronic controlling device are being digitalized in accompany with the development and spreading of the digital control devices such as micro-computers in these days. Therefore, it is strongly desired to provide a power semiconductor device easily controllable by the digital signal from these control devices.
In the above-mentioned power semiconductor device according to the prior art, however, part of a load current is forced to flow through a detecting resistor to detect the load current. Thus, there are generated unnecessary power dissipation and accompanying heat generation in the element itself. It is not always satisfactory for example for use under very severe conditions such as in automobiles. Also, it is not very suited for digitalization.